Dispersive coatings reflect spectral radiation with negligible absorption. Such coatings can be used on furnace interiors for the purpose of increasing fuel efficiency or productivity and for various other applications such as refractory furnace installations, fire screens, hot air ducts, and the like.
A number of reflective coatings have been described. These typically are metal or metal compounds. For example, in U.S. Pat. No. 4,563,843, Grether, et al., suggest silver, gold or copper infra-red reflecting coating as a component of a heat insulation window (column 4, lines 53 to 55).
Laing, et al., disclose a fire resistant enclosure in U.S. Pat. No. 4,174,711. The wall has a reflective layer for infra-red radiation (column 3, line 49). Chromium plating was suggested for this coating, but galvanization in which the outwardly directed surface carries an extremely thin deposit of gold was preferred (id., lines 61 to 68).
In U.S. Pat. No. 4,137,198, Sachs describe a polymer-inorganic hybrid foam comprised of a continuous plastic phase or backbone structure of unexpanded polymer such as polyvinyl acetate, vinyl-acrylic copolymer or asphalt or bituminous pitch, having distributed therein particles of an inorganic phase such as Portland cement or gypsum particles (column 2, lines 7 to 17). The foam was suggested to be useful as a fire-resistant, thermally-insulating construction material (id., lines 40 to 42). At flame temperatures, in some embodiments the surface of the composition developed infrared reflective chromophores from the decomposition of the foam, which acted as mirrors reflecting rays from the surface back to the source of the flame (column 12, lines 21 to 29).
Nolte, et al., disclose a laminated light-transmitting fire screen panel in U.S. Pat. No. 4,104,427. An infra-red reflective coating of a noble metal, copper, aluminum or an oxide may be applied to the vitreous sheet face of the panel (column 4, lines 60 to 63), to help protect it and increase the time taken for the layer to intumesce on the outbreak of a fire.
A similar fire screen glazing panel containing granular intumescent material is described by DeBoel in U.S. Pat. No. 4,268,581. The panels can be coated with an anhydrous metal compound such as zirconium oxide, aluminum phosphate, titanium oxide or tin oxide (column 4, lines 42 to 45 and 60 to 63). Alternatively or in addition, an infra-red reflecting coating of a noble metal, copper, aluminum or an oxide may be applied to protect the intumescent material against radiation absorption and increase the time taken for the layer to intumesce (column 4, line 66 to column 5, line 8).
It would be desirable to have alternate photon-diffusive coatings, particularly more economical coatings than those using expensive noble metals.